Per Ardua Ad Alta at Calder High in Mytholmroyd (by hard work to the heights). I know it has a WP article because it's on my watchlist and I've made a few changes to it. It was one of the the first ever comprehensive schools and appeared in the Guiness Book of Records for a few years for being as such. I'm sure most schools go for mottos that reflect what they'd like the kids to do rather than what they actually do, although I haven't seen one yet with a motto of "sit down, shut up and behave" in any language.